Receiving system



Dec.29, 1936. R. E. MATHES 2,066,047

RECEIVING SYSTEM Filed Aug. 6, 1952 4 Sheets-Sheet l INVENTOR R. E. MATys BY A 2' II ATTORNEY 4 Sheets- Sheet 2 5 is mm m S. E Mm Q OT T m WM, VM I R V.. 5 n H6 W N K K M m M M y g G La g1 0 WV. M48

ATTORNEY Dec. 29, 1936. R. E. MATHES RECEIVING SYSTEM Filed Aug. 6, 1932li 'guia 4 Sheets-Sheet 4 INVENTOR R. E. BY A? f ATTORNEY Patented Dec.29, 1936 RECEIVING SYSTEM Richard E. Mathes, Westfield, N. J., assignorto Radio Corporation of America, a corporation of Delaware ApplicationAugust 6, 1932, Serial No. 627,689

8 Claims. (01. 17888) 4 UNITED STATES PATENT OFFICE The presentinvention relates to receiving systems for use in connection with radioor wire-line transmission.

The invention is particularly applicable to systems for receivingtelegraph signals or image signals for use in reproducing picturerecords.

According to the prior art so far as I am aware, the objection hasfrequently arisen in connection with reproducing transmitted telegraphsignals formed as dots and'dashes that in the space intervening betweensuccessive dots or dashes there was a so-called trailing of the signalwhich tended in reproducing the signals to fill the space betweensuccessive dots so that any two successive dots in a message, forexample, might appear on the record tape as a dash due to the filling inof the spacing period, and thus the message was not readily discernible.

The same objections occur, of course, in connection with thereproduction of pictures by marking with a pen or recording on a lightsensitive record by means of a glow tube, or the equivalent, actuated bythe received signals, so that portions of the picture record whichshould be represented as light gray, for example, may assume a diiferentefiective intensity of representation and appear substantially black.

In the prior art with variable amplitude of sigi nals when a limitingdevice is used to reduce the signals to a uniform amplitude value theinput wave formation loses substantially its true formation due to thecut-ofi action of the limitor device. This does not, therefore, permitaccurate recording and due to the cut-off action makes the length of theresultant marking dependent upon the initial slope of the input wave ascontrolling because the time between the start of each signal-and thetime the cut-off point is reached depends uponthe rate at which thevoltage builds up.

The present invention in its broadest aspects includes an arrangementwhereby the amplitude of the received signals which may vary due toporates as a part thereof a system by which the received signals areintegrated so that it is possible to determine accurately the averageamplitude of the received signals over a'period which is long relativeto an individual dot or dash but is short relative to the intensitychanges usually experienced.

For fast and accurate operation of automatic printers for telegraph workor reproducing equipment for picture work, it is necessary that theproportion of marking to spacing current be maintained relativelyconstant in its efiect upon the reproducing equipment, and it is forthis reason that it is desirable to produce a system to limit theamplitude. of the telegraph or picture signals to a predetermined value,while at the same time not afiecting the ratio of the marking .tospacing periods unduly.

Therefore, as a primary object of this invention I have sought toprovide ways and means by which it is possible to reproduce moreaccurately transmitted code or marking signals.

As a further object of the invention I have sought to provide ways andmeans by which the effect of amplitude variations of controlling signalsrepresenting markings for telegraph work,

or shade values for picture transmission and reception work, may benullified.

As a further object of the invention I have sought to provide a system.which will portray accurately the desired signal indications.

Still a further object of the invention is to provide a simplifiedarrangement for receiving code or other signals which will representaccurately the intended intelligence transmission and, at the same time,provide a system which is relatively simple in its construction andarrangement, as well as a system which can be con-' structed compactly,and which will utilize existing apparatus re-designed to produce thedesired results.

Other and further objects and advantages of the invention will becomeapparent to those skilled in the art to which the invention relates byreading the following specification and claims in connection with theaccompanying drawings,

wherein:

Fig. 1 illustrates a preferred form ofcircuit arrangement serving toproduce the desired results above enumerated;

-.Fig. 2a' indicates an assumed form of input wave an amplitudesubstantially three times that of the wave of Fig. 2a;

Fig. 3a indicates the practical effect of the circuit shown by Fig. 1 toproduce 'a marked decrease in the variation of spacing to markingindications with variations in the input voltage;

' Fig. 3b is the same general wave shape as shown by Fig. 3a. butapplied to the input wave formation shown by Fig. 2b;

' Fig. 4a indicates the curves for screen current plotted against screenvoltage with the biasing limiter tube shown and described by Fig. 1;and,

Fig. 4b is a series of curves plotted to represent the plate currentplotted against the screen voltage for the automatic bias limiting tubeof Fig. 1.

To refer now specifically to the various figures of the drawings,reference may first be made to Figs. 2a and 2b where in Fig. 2a there isrepresentedan input wave shape to energize the circuit including a biaslimiter. The input wave is of such formation that the wave formationitself controls to a considerable extent and would, with apparatusnormally used to reproduce the input signals, produce in the outputcircuit the effect of differing input wave shapes. By this figure, theline AA represents one setting of a limiting device of the type known tothe art as a cutoff limiter wherein the cut-off is such that it occursat about 75% of the input voltage which results in approximately 31%marking period for each impulse, and line BB represents the cut-off atapproximately 50% of the input voltage, so that the marking impulses areof a duration approximately 44% of the actuating signal duration.

The same general wave shape is illustrated by Fig. 21) except that thewave formation is of approximately three times the amplitude of the waveshown by Fig. 2a, so that'the marking period with the bias limiter setat the level indicated.

as A-A is approximately 58 of. the complete dot cycle and with the biaslimiter set to a value corresponding to the voltage indicated by theline BB will be approximately of the complete dot cycle. I

From these figures, it is'quite apparent that the plate current of thelimiting tube will be for the cut-off points AA or BB along the lineOA-A-l00 or O-B--BI00.'

Any recording device which may be operated by the limiter would show acomparative portion of marking to spacing corresponding substantially tothat shown by Figs. 2a and2b, and in such a case the marlaing percentagevariation, when using ink recorders, relay operated devices, automaticprinters, or glow tubes, or similar apparatus, would have a seriouseffect uponthe produced record. In cases where the recorder apparatus isused with the 31% marking period above shown,

that for fast and accurate operation of automatic printers or facsimilereproducing equipment that Y the proportion of marking to spacingcurrent be maintained relatively constant, and it is to overcome thesedifficulties that the arrangement shown by Fig. 1 has been developed.

To refer now particularly to the preferred circuit arrangement which isshown by Fig. 1, input voltages which are transmitted to the reproducingequipment from a receiver line or as a rectified radio signal may beimpressed across the terminals ll, and after passing through a suitablefiltering apparatus 3, which includes series inductance elements 5 andshunt capacities I, may

be impressed across a resistor element 9, or the equivalent, upon anamplifying tube II. A part of the output from the amplifier I I in theform of a pulsating direct current signal is then supplied to a secondamplifying tube 13, which is herein termed an integrating, reversingtube.

After suitable amplification the signal is then impressed through aresistor l5 upon the control electrode I! of the automatic bias limitertube 19. C nnected in parallel with the input circuit of t e automaticbias limiter tube I9 is what I have termed an integrating circuit. Thiscircuit includes parallelly connected capacity and resistance elements2| and 23 respectively, which is for the purpose of integrating orsmoothing out the variations caused by the keying as impressed by way ofthe input signals supplied to the terminals l-I, so as to leave onlythe'longer period variations which are caused by actualfluctuations inthe mean amplitude of the input signals.

In opposite phase to the signalssupplied through the integratingreversal tube ii to the control grid I! of the tube Hi, the same signalsappearing in the output circuit of the amplifying tube II are directedto the screen grid'25 of the screen electrode Here degrees out-of-phasewith respect to thevoltagesappearing upon the control electrode ll ofthis tube, which is due to the fact that the voltages on the controlelectrode ll have been passed through the amplifier or integratingreversal tube l3, whereas the voltages upon the screen electrode havenot been so amplified. According to this arrangement, therefore, it isseen that the integrating variations of the input voltage in properphase are directed to. the inner or control grid of the screen grid tubel8 so that this controlled grid acts merely as a secondary grid toprovide an automatic bias for the remaining elements of the tube, andthe screen grid, which is connected with the plate circuit of the firstamplifying tube ll, controls the plate current flow from this automaticbias limiter tube as modified in accordance with the bias on the inneror control grid H which results from the action of the integratingcircuit including the capacity andresistance elements 2| and 23.

' Connected with the output of the tube l9 are a pair of push-pullconnected amplifying tubes 2l and 29 respectively which serve merely asrelay tubes used to amplify the output from the screen grid tube and toproduceapush-pull action. The output from these push-pull. connectedtubes 21 and 29'appears across the output terminals II. Also connectedwith the output circuit of the push-pull amplifying tubes 21 and 29 is apotentiometer 30 which provides a manual control or adjustment by whichthe operator may adjust the output for different marking and spacingconditions so that in one case more power will be transferred to 'theload circuit than in another case. This will have the effect, ,when' thecircuit is used to operate a relay or other suit.-

adjustment of the transmitting relay, by multipath radio signals, bydistortion in landlines or other similar causes.

The filter system 3, which is in the nature of a low-pass filter, servesmerely to smooth the action of the system and is not at all essential tothe operation. As shown herein, all tubes are supplied with heatingcurrent from a common source connected at the terminals 33 and 35 andgrounded at the point 31. Similarly, suitable biasing potentials for thegrids may be supplied from a terminal 39 and plate voltages may besupplied from a terminal M. In each case, appropriate bias resistors,not specifically identified by numerals, are arranged to control thescreen and plate voltages in any desired manner.

, The'operation of the system it is believed will be quite apparent fromthe foregoing description, but for purpose of further explanationreference may be had to Figs. 4a and 4b of the drawings which illustratethe D. C. characteristics of the usual screen grid tubes when resistorsare included in both the plate and screen grid leads. It is to be notedin connection with these figures that the screen voltage plate currentcharacteristics have decreasing slopes with increasing negative bias onthe control grid. It is seen, furthermore, that these characteristicsreach a certain maximum value at which they flatten otf completely.Thus, if a signal of any given wave shape is applied to the screen gridand the amplitude held below the limiting curvature, the plate currentwill approximate the same wave shape, providing the proper directcurrent voltage is supplied to the control grid. If the input amplitudeis then increased considerably, the plate current output will remainsubstantially the same as before, provided the control grid directcurrent voltage is properly modified. If

such modification of the control grid voltage can be accomplishedsimultaneously with variation of amplitude of the input wave shape, thenthe device, it will be seen, can function satisfactorily as a limiterwhich produces substantially constant output of the original wave shaperegardless of the amplitude of the input voltage, as was described inconnection with the description of the system shown by Fig. 1.

If now in the circuit shown by Fig. '1 the input amplitude increasesbeyond the limit provided for automatic adjustment of the control griddirect current bias, then, due to the saturation limiting indicated bythe curves shown by Figs. 4a and 4b, the circuit of Fig. 1 will commenceto act as a saturation-limiter and will cause the marking to spacingratio to increase in a manner similar to the action of a cut-otIlimiter. This action, however, is superimposed upon the bias limitingaction previously explained, with the net result of very greatlyenlarging the range of input amplitude necessary to produce a givenrange of variation in the marking to spacing ratio. It should be notedin connection with this description, however, that the normal operatingrange of the device is intended to be confined below the point wherethis saturation-limiting? takes eflect.

By Figs. 3a; and 3b, the practical effects of the circuit shown by Fig.1 have been illustrated, and comparison with the wave formation shown byFigs. 2a and 2?), show a very marked decrease in the variation ofmarking to spacing ratio with a variation of input voltage.

In connection with the showing of Figs. 3a and 3b, it should beunderstood that the wave formations illustrated by Figs. 2a and 2brespectively may be considered merely as examples of the input waveshapes supplied to the automatic bias limiter circuit. It isparticularly interesting to note that whereas increasing amplitudeincreases the marking to spacing ratio in a cut-oil type of limiter itdecreases that same ratio in the bias limiter herein disclosed. Thisoffers a considerable advantage in practical operation as increasingamplitude of the incoming wave is often accompanied by a truelengthening of the signal wave shape, and in the automatic bias limiterherein disclosed the two efiects 'will tend to practically offset eachother, and this, it will be seen, results in a more uniform length ofcharacter appearing in the output circuit-which is connected to theterminals 3i. This output circuit, which has not been specificallyshown, will include, as above stated, either an automatic telegraphprinter, ink recorder, glow tube, or relay operated devices.

While the invention has herein been disclosed in only one of itspreferred forms, it is nevertheless to be understood that from apractical viewpoint, many and various modifications may be made andstill retain the broad scope of the basic principles taught by thisdisclosure. I, there fore, believe myself to be entitled to make and useany and all modifications of the arrangement herein disclosed, provided,of course, such modifications fall fairly within the spirit and scope oithe invention, as defined by the hereinafter appended claims.

Having now described my invention, what I claim and desire to secure byLetters Patent of the United States, is as follows:

1. A signalling system including an input circult, an output circuit anda multi-electrode thermionic, device coupling the input and outputcircuits, means for supplying signals appearing in the input circuitdirectly upon one of the pin-- vice irrespective of the intensityfluctuation in' the input signals is maintained.

2. In a limiting device, a multi-electrode limiting thermionic tube,means for supplying signals to one of the electrodes of said tube,polarity reversing means parallelly connected with said first namedmeans, integrating means connected to said polarity reversing means, andmeans for connecting the integrating means to a second one of theelectrodes of said tube, whereby substantially constant amplitude outputenergy irrespective of fluctuation in average amplitude of the suppliedsignals is maintained.

3. In a system for obtaining constant level output energy, a signalsource, a load circuit, and a multi-electrode thermionic tube forsupplying signals to the load circuit, means for applying signals to onecontrol electrode of the multi-electrode tube, polarity reversing meansparallelly connected to said first named means, integrating meansconnected to the polarity reversing means, and means for connecting theintegrating means to a second control electrode of the multi-electrodetube.

4. An energy transfer system comprising a thermionic tube having aplurality oi cold electrodes, means to supply input signals of fiuct'irating amplitude to one of said cold electrodes, polarity reversing meansparallelly connected to said first named means, energy integrating meansconnected to said polarity reversing means, and

means for connecting said integrating circuit to the control electrodethereof connected with the input circuit so as to have the inputsignalsimpressed thereupon, an integrating circuit connected across theinput circuit to integrate the supplied signals so as to varyautomatically the bias level of the thermionic device, means to supplyto a second control electrode of the thermionic device the integratedinput signals in substantially phase opposition to the signals suppliedto the first control electrode to produce from the thermionic devicesubstantially constant amplitude output energy, and a load circuit forutilizing the output energy from the thermionic device.

6. In a signalling system for maintaining constant amplitude outputenergy and establishing 1 a predetermined ratio between marking andspacing for telegraph communication, an input circuit having impressedthereon signals of fluctuating intensity varying between zero and avariable amplitude, a thermionic device having the control electrodethereof connected with the input circuit so as to supply the inputsignals thereto, and integratingv circuit including a parallel connectedresistor and capacity element connected across the-input circuit tointegrate the supplied signals so as to vary automatically the biaslevel of the thermionic device, means to supply'to a second controlelectrode of the thermionic device the integrated input signals insubstantially phase opposition to the signals supplied to the firstcontrol electrode to produce from the thermionic device substantiallyconstant amplitud output energy, and a load circuit for utilizing theoutput energy from the thermionic device.

7. In a signalling system for maintaining constant amplitude outputenergy for telegraphic communication, an input circuit having impressedthereon signals of fluctuating intensity varying between zero and avariable amplitude, a thermionic device having the control electrodethereof connected with the input circuit so as to supply the inputsignals thereto, an integrating circuit connected across the inputcircuit to integrate the supplied signals so as to vary automaticallythe bias level of the thermionic device, means to supply to a secondcontrol electrode of the thermionic device the integrated input signalsin substantially phase opposition to the signals supplied to the firstcontrol electrode to produce from the thermionic device substantiallyconstant amplitude output energy, a push-pull amplifying stage connectedwith the output .of the said thermionic device, a load circuit connectedwith the output of the push-pull amplifier, and a potentiometerconnected across the load circuit to unbalance'to a predetermined degreethe push-pull stage 'to compensate for discrepancies between the lengthof markings and spacing of certain of the impressed signals.

8. In a signalling system, an input circuit, an output circuit, anamplifier connecting said input circuit with said output circuit, saidampliher having at. least two cold input electrodes, two parallellyconnected signal controlled input circuits, means for directlyimpressing on one 01" the input electrodes one of the parallel inputs,and means for impressing an integrated version of the signal on theother input electrode from the other input circuit.

RICHARD E. MATHES.

